Frequency dividing circuit,with semiconductors



FREQUENCY DIVIDING CIRCUIT, WITH SEMICONDUCTORS Filed Feb. 5, 1967 April7, 1970 ERIC-ANDRE VITTOZ 3 Sheets-Sheet 1 April 1970 ERIC-ANDRE VlTTOZ3,505,536

FREQUENCY DIVIDING CIRCUIT, WITH SEMICONDUCTORS Filed Feb. 5, 1967 '5Sheets-Sheet 2 April 7, 1970 ERIC-ANDRE VITTOZ 3,505,536

FREQUENCY DIVIDING CIRCUIT, WITH SEMICONDUCTORS Filed Feb. 5, 1967 3Sheets-Sheet 5 United States Patent Oifice 3,505,536 Patented Apr. 7,1970 land Filed Feb. 3, 1967, Ser. No. 613,937 Int. Cl. H03k 21/04 US.Cl. 307225 1 Claim ABSTRACT OF THE DISCLOSURE A frequency dividingcircuit comprises a source of periodic input signals whose frequency isto be divided, a semiconductor switch means, a condenser, and anunstable multivibrator. The frequency of the output signal of themultivibrator is variable under the control of a voltage existing at theterminals of the condenser. The terminals of the condenser areperiodically connected to the terminals of the source of the periodicinput signals by the closing of the semiconductor switch means which isclosed in synchronism with the output signal of the unstablemultivibrator. Thus, the frequency of the output signal is brought underthe control of a submultiple of the frequency to be divided.

The present invention has for object a frequency dividing circuit, withsemiconductors.

Frequency dividing circuits are already known in which the phase of avariable frequency oscillator is brought under control.

The purpose of the invention is the realization of such a circuitworking under low power and capable of being produced in the form of anintegrated circuit.

The circuit according to the invention is characterized in that itcomprises an unstable multivibrator the output signal frequency of whichis variable under the control of a voltage existing at the terminals ofa condenser, which is branched periodically and for a short moment tothe terminals of the source of the periodic signal the frequency ofwhich must be divided, by the closing of an electronic circuit-breakercontrolled in synchronism with said output signal, the whole so as tobring the frequency of this output signal under control cf asub-multiple of the frequency to be divided.

The accompanying drawing shows, by way of example, four embodiments ofthe circuit object of the invention.

FIG. 1 is a general diagram of the circuit.

FIG. 2 is an explanatory diagram of the operation of the circuit shownin FIG. 1.

FIGS. 3 to 6 show in detail four different embodiments.

The circuit shown in FIG. 1 comprises an unstable multivibrator Mproducing a periodic signal a The frequency P of this signal isadjustable by an adjusting voltage 11 memorized in a capacity C.

An electronic circuit-breaker I, which is closed at each period of thesignal 1: for a short moment, applies the source of the periodic inputsignal ii of frequency F and internal resistance R to the terminals ofthe capacity C. This has for effect to charge the latter to a voltage 11depending upon the relative phase of the signals u and u In other words,in equilibrium, the voltage 11 is equal to the value of 11 at themoments when the signal u passes a well determined phase, in the caseshown in FIG. 2, at the moments when the commutation of themultivibrator changes from one state to the other. The middle part ofFIG. 2 indicates the position of the circuit-breaker I. At Q, one hasthe open position and at F, the closed position. In the three parts ofthis FIG. 2, r designates the time axis.

If the circuit is suitably dimensioned, it is possible to put the outputfrequency F into step with a submultiple of the input frequency F Thetwo frequencies remain in step if one slowly varies the frequency Fbetween certain limits. As a matter of fact, a variation of F produces avariation of the relative phase of the signals u and 11 thus a variationof the adjusting signal 11 This latter acts on the frequency P of thesignal a so that F follows the variations of F In the case of FIG. 2,the ratio n of the frequencies F and F is three.

The circuit permits of obtaining ratios :1 of several hundreds.

FIGURE 3 shows the detail diagram of a first embodimerit.

The multivibrator Ma comprises two transistors T T of the type NPN,interconnected between base and collector by condensers 1a and 2a. Theiremitters are connected to the negative pole of a voltage source whereasthe collectors are connected to the positive pole of the latter by tworesistances 3a, 4a. The control voltage 14 is applied to the commonpoint of the two resistances 5a and 6a the other ends of which areconnected to the bases of the transistors T and T From the theory ofmultivibrators it is known that the frequency of the latter may bevaried by varying the voltage 11 The circuit-breaker Ia comprises a PNPtype transistor T the base of which is connected to a circuit Rda-Cda,which permits of obtaining in the base of T current impulses which arethe derivatives of the rectangular impulses created at the collector TThe source of the input signal 11 is branched between a terminal of thecondenser Ca and the collector of T the other terminal of the condenserCa as well as the emitter of T being connected to the positive pole ofsaid voltage source.

The circuit operates in the following manner:

The multivibrator Ma creates rectangular impulses of which therepetition frequency depends upon the voltage 11 The circuit CdaRda:produces a short current impulse at the base of the transistor T which,thus, becomes conducting and branches the source of the input signal ato the terminals of the condenser Ca which charges at a voltage 14tending towards the instantaneous value of u at the moment of theimpuse. This voltage 3a, memorized until the apparition of the followingdifferentiated impulse, is applied to the common point of the basicresistances of the transistors T and T and thus controls the frequencyof the multivibrator.

In the following embodiments, the elements similar to those of FIG. 3are designated (in order to shorten the description) by the samereference signs, no longer with the sign a, but the sign b for FIG. 4, cfor FIG. 5 and d for FIG. 6.

The circuit shown in FIG. 4 differs from the preceding one in that itonly comprises transistors of a same type NPN. To this end, a currentreverser Iv consisting of a transistor T and of two resistances 7b and8b is inserted between the multivibrator Mb and the differentiation circuit Cdb-Rdb of the circuit-breaker lb of which the collector of thetransistor T is fed through the agency of a diode 10b. The source of theinput signal a is branched between the negative pole of the supplysource, which constitutes a common earth, and a connecting condenser 9b.Independently of the use of transistors of a same type, this embodimenthas the advantage of permitting the use of an input signal source ahaving a point which is earthed.

In the embodiment according to FIG. 5, one has inserted in themultivibrator Mc tWo resistances 11c and and two diodes 13c and 14c inorder to stabilize the frequency thereof against variations of the feedvoltage or of the temperature.

There modifications further permit of economizing the reverscrtransistor T of FIG. 4. On the other hand, the voltage at the terminalsof the condenser Cc is applied to the multivibrator through the agencyof an additional transistor T which permits of working with a source ofu the internal resistance of which is high and a capacity Cc of lowvalue.

A fourth example is shown in FIG. 6. The base circuit of the reversertransistor T has been improved in order to obtain a steeper positivefianc signal at the collector and thus a more precise checking,necessary for a high input frequency. This improvement consists inattacking the base by a resistance 7d, a diode 15d and a capacity 16:1in parallel.

The use of a common emitter amplifier stage T542 permits of working witha high internal resistance R of the source u and a low capacity 9a, withthe advantage over the circuit of FIG. 5 of not lowering the averagelevel of the control signal u (which is of great importance if thecircuit must work with a low feed voltage). One realizes simultaneouslya compensation for the effects of temperature variations and feedvoltage.

The feed of the collector of the transistor T is eifected by a voltagedivider 17d, 18d, the feed of the transistor T being effected throughtwo resistances 19d and 20d.

What I claim is:

1. A frequency dividing circuit comprising a source of periodic inputsignals, means for dividing the frequency of said periodic inputsignals, said dividing means comprising a semiconductor switch means, anunstable multivibrator, a condenser, means serially conductivelyconnecting said source of periodic input signals to said semiconductorswitch means, means serially conductively connecting said semiconductorswitch means to said unstable multivibrator, means conductivelyconnecting said condenser between said source of periodic input signalsand said unstable multivibrator, means conductively connecting saidcondenser in parallel with said. semiconductor switch means, a feedbackpath conductively connecting the output signal of said unstablemultivibrator to said semiconductor switch means, means for periodicallyclosing said feedback path in synchronism with said output signal fromsaid unstable multivibrator in order to com ductively connect saidcondenser to said source of periodic input signals through saidsemiconductor switch means whereby said condenser varies the frequencyof said output signal under the control of a subrnultiple of thefrequency to be divided.

References Cited UNITED STATES PATENTS 2,866,104 12/1958 Biggam 307-455JOHN S. HEYMAN, Primary Examiner B. P. DAVIS, Assistant Examiner U.S.Ci. X.R. 307247, 291

